What’s Killing the Dolphins?

In Norfolk, Va., team members from the Virginia Aquarium record observations last week on the third dolphin body they retrieved in one day.

The Virginian-Pilot/Associated Press

Dolphins are washing up dead along the East Coast this summer, perplexing scientists who fear a recurrence of a large-scale die-off several decades ago.

A federal government group is scrambling to identify possible causes for the deaths seen from New York to the Chesapeake Bay. Among the suspects, depending on the location, are viruses, bacteria, biotoxins—poisons produced by algae—environmental changes, pollution and injuries from ships and fishnets. There is no indication the deaths in the various regions are related.

In July alone, teams in New York, New Jersey, Delaware, Maryland and Virginia recovered 91 dolphin bodies, according to the National Oceanic and Atmospheric Administration. In July 2012, teams in those states found only 10 dead dolphins.

Virginia found 49 dolphins in July—the norm for the month is seven. Maryland has had 15 dolphin deaths this year, about double the normal amount.

Marine mammal experts worry that the incidents may be the beginning of a widespread rise in dolphin mortality, similar to one of the late 1980s, when almost 800 dolphin bodies washed up on beaches from New Jersey to Florida. Scientists theorized that event was caused either by a biotoxin stemming from algae, or a virus similar to distemper.

“It’s very alarming,” said Trevor Spradlin, a NOAA marine mammal biologist. “The fear is if there is a massive disease outbreak or contamination outbreak, that it could have a serious impact on a local [dolphin] population or even a broader portion of the population.”

The die-off of the bottlenose dolphins () in the mid-Atlantic comes as scientists still are trying to explain a rise in bottlenose dolphin deaths in Florida’s Indian River Lagoon, which began in January, and in parts of the Gulf of Mexico going back to 2010.

In Florida, investigators are looking at an algae bloom as a possible cause, and in the Gulf, NOAA scientists and others are looking to see if the 2010 Deepwater Horizon spill, which occurred after the die-off began, may have played a role in making it worse.

A rise in dolphin mortality in Australia this year was linked to a virus, but so far scientists have found no indication the U.S. outbreaks are related to it.

Bottlenose dolphins aren’t on NOAA’s endangered species list. NOAA estimates 39,000 bottlenose dolphins live off the East Coast, and about 13,500 off the Gulf Coast.

Environmentalists are concerned what the deaths of dolphins, among the ocean’s top predators, might mean for the marine food chain and whether the dolphins may be eating fish that are making them sick.

“When the bigger predators are dying, they’re not the canary in the coal mine. Frankly, they’re the miner,” said Casi Callaway, executive director of the Alabama environmental group Mobile Baykeeper. “Dolphins are what we’re seeing wash ashore. What else is being affected?”

NOAA’s working group on unusual deaths among marine mammals—a panel of government oceanographic experts, academics and veterinary scientists—is gathering to respond to the mid-Atlantic deaths, and experts from around the country are coming to help, said Mr. Spradlin.

Mark Swingle, director of research and conservation at the Virginia Aquarium & Marine Science Center in Virginia Beach, has been leading teams rushing to beaches across the Chesapeake Bay to recover dolphin carcasses, which they take to labs for autopsies. The region usually averages about 65 dolphin corpses a year, but by early August the teams had recovered more than 100, he said.

“We’re assuming that it’s some sort of disease process; we just don’t have any idea what that is,” he said.

The symptoms are varied. In Florida’s Indian River Lagoon, the dolphins are emaciated. In Virginia, they are of regular weight. In the Gulf, some are gaunt and frail.

The Indian River Lagoon usually sees two or three dolphins die a month. Since January, that rate has tripled. Dead manatees and birds were found after an algae bloom in 2011, and researchers think a bloom may be to blame for the dolphin deaths.

The deaths in the Gulf apparently aren’t related to any direct human contact, like propeller injuries or drownings in fishing nets. But three years after the deaths began, NOAA still doesn’t know the cause of “a very strange phenomenon,” said Mr. Spradlin. “And we don’t know to what extent the Deepwater Horizon exacerbated the event.”

Mr. Swingle in Virginia has been driving along the coast all summer to track down dolphin corpses, most of which are decayed by the time he or his staff arrive. He remembers recovering dead dolphins during the large die-off in 1987 and 1988, and this year feels eerily similar, he said.

“We’re early into this, but it’s certainly reminiscent of that period,” he said.